Optical multiplexers and de-multiplexers may be considered to be key components in wavelength division multiplexing (WDM) networks for optical interconnects. To send multiple wavelengths (sometimes referred to as “channels”) down a single optical fiber, the wavelengths must be multiplexed (i.e., combined) by a multiplexer at one end and de-multiplexed (i.e., separated) by a de-multiplexer at the receiving end. Generally, multiplexer and de-multiplexers that use an echelle grating may be used due to their compact size, lower cost, and their integration ability with other optical components like lasers and detectors.
More specifically, example hybrid integrated transmitters may include a laser, modulator, multiplexer, and one or more passive components on the same silicon substrate chip. On-chip back reflected light from each component may interface coherently and inherently, and degrades the laser transmitter stability in laser relative intensity noise (RIN) and laser side-mode suppression ratio. This degradation may lead to bit error rate (BER) floor generation and transmitter performance degradation over the device operating window.
Similarly, the receiver may include a photodetector, de-multiplexer, and one or more passive components on the same silicon substrate chip. On-chip reflected light from the de-multiplexer and the passive component(s) may interface coherently and inherently, and generate a multi-path interference effect. This multi-path interference effect may produce additional noise at the receiver.
Legacy total internal reflection echelle grating solutions could produce higher back reflection of light to the laser and detectors, resulting in laser instability at the transmitter or additional noise at the receiver.